1. Field of the Invention
Embodiments described herein relate generally to a magnetic resonance imaging apparatus and an RF coil device.
2. Description of the Related Art
MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) set in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation. The aforementioned MRI means magnetic resonance imaging, the RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal.
Here, an RF (Radio Frequency) coil device is a device which transmits an RF pulse to nuclear spin inside an object by, for example, supplying a coil with an RF pulse electric current and detects generated MR signals.
Some of RF coil devices are built-in an MRI apparatus and other RF coil devices are recognized by a control unit of the MRI apparatus by being connected to a connection port of the MRI apparatus such as local RF coil devices, for example.
In MRI, multi-channel structure is promoted in acquisition system of MR signals. The above “channel” means each pathway of a plurality of MR signals outputted from each coil element and inputted to an RF receiver of an MRI apparatus. Although the number of channels is set to equal to or smaller than the input reception number of the RF receiver, a large number of RF coil devices can be connected to an MRI apparatus.
If the number of cables between an RF coil device and an MRI apparatus increases due to promotion of the aforementioned multichannel structure, it is inconvenient because hard-wiring becomes complicated.
Therefore, it is desired to unwire transmission and reception of signals between an RF coil device and an MRI apparatus. However, radio communication by an analogue signal has not been achieved, because there are various restrictions such as degradation of dynamic range.
More specifically, in order to suppress influence on receiving sensitivity to weak MR signals emitted from an object, it is impossible in an MRI apparatus to enlarge the output of electromagnetic waves used for radio communication between an RF coil device and an MRI apparatus.
If it is impossible to enlarge the radio output power, dynamic range degrades due to signal loss caused when transmitted signals travel space. Then, in Japanese Patent Application Laid-open (KOKAI) Publication No. 2010-29664, digital radio communication method in which MR signals are digitized and then transmitted wirelessly is proposed.
Although the problem of restriction of dynamic range can be solved by wirelessly transmitting MR signals after digitalization, this method has the following problems.
Firstly, regulation of radio communication is different from country to country, and the same transmission frequency or the same transmission power can not be necessarily used in other countries.
Secondly, if MR signals are wirelessly transmitted from an RF coil device to an MRI apparatus, the transmitted radiowaves are reflected off surrounding areas and this degrades own data of radio communication.
Therefore, novel technology to wirelessly transmit digitized MR signals from an RF coil device to an MRI apparatus satisfactorily has been desired in MRI.